Case study on the turbulent motion properties and its effect on heat transport during a haze event by the quadrant method

Abstract

Based on the high-frequency measurement data of three-dimensional wind speed and temperature during the haze period, the turbulent motion and its influence on the heat transport process were revealed. Our results show that the results of the initial and decay stages of the haze event are qualitatively consistent with the results during the sunny days, and are close quantitatively. The difference of turbulence between haze events and sunny days is mainly reflected in the development stage of haze events. For fluctuations with a period greater than 1 h, with the development of the haze event, the large-scale fluctuation value of vertical wind speed increases, which can reach 0.65 m/s; the peak value of temperature fluctuation decreases; turbulence intensity of vertical wind speed, shear stress and vertical heat flux increase; the outward interaction events dominates the turbulent motion and the upward transportation of hot air. For fluctuations with a period of less than 1 h, as the PM10 concentration increases, the vertical heat flux gradually decreases; the diurnal changes of the shear stress will change qualitatively, that is, the shear stress first increases and then decreases; on the whole, the number of outward interaction events and inward interaction events in the development stage of haze events is greater than the number of ejection events and sweeps events; quantitatively, the flux peaks of events corresponds to upward transportation of high-speed hot air, upward transports of high-speed cold air, downward transport of high-speed hot air and downward transports of high-speed cold air decrease with the development of haze events. Therefore, the turbulent motion of different scales needs to be considered in the study of the haze events.